1. Field of the Invention:
The present invention relates to a disc cutting apparatus for cutting at least one surface of a disc-shaped workpiece which is being rotated, while pressing an outer circumferential surface of the workpiece at a plurality of locations thereon with a plurality of holder mechanisms to preventing the workpiece from swinging in the circumferential direction thereof and also from being displaced in the axial direction thereof.
2. Description of Background Art:
Disk-shaped workpieces such as disc rotors for use in automobile disc brakes are required to have parallel and flat surfaces on the both sides. Attempts have been made to hold disc rotors parallel to cutters while cutting the disc rotors, but they have proven unsatisfactory.
Disc rotor cutting apparatus are disclosed in Japanese laid-open patent publications Nos. 62-218042 and 59-37002 and U.S. Pat. No. 4,266,454, for example.
According to Japanese laid-open patent publication No. 62-218042, a sleeve has a cylinder defined therein and a rod with a piston movably disposed in the cylinder, the sleeve and the rod being coaxially placed in a body. Stoppers for controlling the strokes of the sleeve and the rod are attached to an outer end of the body, and tool bits are mounted on the other outer end of the body for simultaneously cutting the opposite surfaces of a disc rotor.
According to Japanese laid-open patent publication No. 62-218042 or U.S. Pat. No. 4,266,454, two cutter bases are fitted over a main spindle and support respective tool bits thereon. The opposite surfaces of a disc rotor are simultaneously cut by the tool bits while the disc rotor is rotating between the tool bits.
In the conventional disc cutting apparatus, the center of the disc rotor is required to be fitted over the main spindle perpendicularly thereto when the disc rotor is rotated and cut by the tool bits. If the disc rotor were slightly tilted with respect to the main spindle, the circumferential edge of the disc rotor would periodically be displaced axially, i.e., rotate in a tortuous path, with resulting chattering of the disc rotor. Therefore, the opposite surfaces of the disc rotor would have a chatter mark and not be machined to a smooth finish.
Removal of such a chatter mark requires the opposite surfaces of the disc rotor to be machined again by the disc cutting apparatus. Therefore, the entire process of cutting the disc rotor is lengthy and complex, and the rate of production of disc rotors is relatively low.